The National Education Association, the nation’s largest labor union, says that more than 1 million people have used an online form during the past three weeks to email their senators to urge opposition to Betsy DeVos, President Trump’s nominee for education secretary. More than 40,000 people have called senators using a hotline the union set up to access the switchboard at the U.S. Capitol, NEA officials said.

NEA President Lily Eskelsen Garcia said the union did not pay for advertisements, instead using its ordinary advocacy channels — such as emails to members and social media posts — to encourage people to contact their senators. She said the response surprised and gratified her.

“It’s just amazing,” Eskelsen Garcia said. “We couldn’t generate this if it weren’t authentic, if it weren’t something legitimately and authentically viral.”

The pace of calls and emails about DeVos surpasses any previous NEA campaign, union officials said: In all of 2015, efforts to get teachers to contact Congress about the Every Student Succeeds Act — a sweeping new federal education law that affects every public school in the nation — generated a total of 284,000 emails, they said.

The NEA’s figures come from internal data generated through a CQ-Roll Call advocacy outreach tool, called Engage. CQ-Roll Call confirmed that NEA campaigns to contact lawmakers during the past 30 days have generated nearly 1.1 million emails and almost 3,000 tweets.

And there are signs that DeVos’s nomination has helped generate a higher-than-usual volume of calls and emails to the offices of senators who will decide whether she is confirmed as education secretary.

A spokeswoman for Sen. Tim Kaine (D-Va.) said his office has received more than 25,000 calls or emails related to DeVos, and the vast majority have been opposed to her joining Trump’s Cabinet.

A spokeswoman for Sen. Lisa Murkowski (R-Alaska) said her office has received more calls than usual in the past week, and that the majority of callers have been asking Murkowski to vote against confirming DeVos. Most of the callers are not Murkowski’s constituents, the spokeswoman said.

A spokeswoman for Sen. Michael F. Bennet (D-Colo.) said his office is receiving more calls than usual. “We are grateful that our constituents are speaking out and getting involved,” she said. “We have a team of constituent advocates who are listening and gathering feedback.”

Bennet, Kaine and Murkowski are members of the Senate Committee on Health, Education, Labor and Pensions, which must approve DeVos’s nomination before the full Senate can vote. A committee vote is scheduled for Tuesday.

Spokespeople for more than a dozen other senators did not respond to requests for comment. No Republicans have said they will defect, suggesting DeVos is still very likely to win confirmation.

Sen. Charles E. Schumer (D-N.Y.), the Senate minority leader, joined a growing chorus of Democratic pledging to vote against DeVos, putting out a statement Thursday morning saying he will “vote no, and I will do it proudly”:

“The President’s decision to ask Betsy DeVos to run the Department of Education should offend every single American man, woman, and child who has benefitted from the public education system in this country. Public education has lifted millions out of poverty, has put millions in good paying jobs, and has been the launching pad for people who went on to cure disease and to create inventions that have changed our society for the better.

“Betsy DeVos would single-handedly decimate our public education system if she were confirmed. Her plan to privatize education would deprive students from a good public education, while helping students from wealthy families get another leg up. It would deprive teachers of a decent salary, and it would make it harder for parents to get a good education for their kids.

“Betsy DeVos would be just another member of the swamp cabinet that is full of billionaires and bankers. The fact that she refuses to divest from companies that would line her family’s pocket as education secretary, while crushing students with additional debt is all the proof one needs to know that she is in this for herself, and not for students.”

DeVos is a Michigan billionaire who has spent most of the past three decades using her clout and her wealth to advocate for the expansion of taxpayer-funded voucher programs and charter schools. The nation’s two major teachers unions have vigorously opposed her nomination from the start, calling her an enemy of public education with no qualifications for the job of education secretary.

DeVos’s supporters say that she is a bold reformer who is dedicated to taking on unions and the entire education establishment, if that’s what it takes to ensure that more children — especially those from low-income families — have access to good schools.

But opposition to DeVos appeared to spike after her Jan. 17 confirmation hearing, during which she stumbled over basic education policy, declined to promise that she wouldn’t try to privatize public schools and passed up a chance to reassure senators that she would not seek to rein in the Education Department’s Office for Civil Rights. She also said she opposes a blanket ban on guns in schools — citing one example of a rural school that might want to protect against “potential grizzlies” — a statement that brought near-immediate ridicule from late-night comics.

DeVos acknowledged that she and her family members have probably donated at least $200 million to Republicans over the years, and Sen. Bernie Sanders (I-Vt.) who sought the Democratic nomination for president, asked her at the hearing if she thought she’d be a nominee if not for those donations; she said she would be either way. The teachers’ unions are regular contributors to Hill Democrats, and the NEA was an early endorser of Democrat Hillary Clinton in her presidential bid.

Some protesters at Saturday’s Women’s March on Washington carried anti-DeVos signs, and liberal filmmaker Michael Moore exhorted the hundreds of thousands in attendance to call their senators every day to voice opposition to the Education nominee. More than 250,000 people have signed a Change.org petition opposing her nomination.

Eskelsen Garcia, the NEA president, said that the pushback matters — even if DeVos does end up winning confirmation from the Senate.

“We now have more activists that we can activate on a moment’s notice when we need them,” she said. “They’ve told us, ‘This is vital to us, this is important to us, we are passionate for this.’ And they will want to hold people accountable, from Donald Trump to Betsy DeVos to the senators who made it possible for her to have that kind of power.”